1. Field of the Invention
The present invention relates to portable radiotelephones and other mobile communication devices and a method for setting the automatic frequency control (AFC) initial value for an AFC function.
2. Description of the Related Art
Portable radiotelephones are generally configured as shown in FIG. 10. That is, signals received via the antenna in the radio component (101) are subjected to down-conversion, delayed wave detection and demodulation, then digitized in the A/D, D/A converter (102) and sent on to an ASIC (application specific LSI) signal processor (103).
The ASIC signal processor (103) detects phase errors, and regenerates the clock and received data, then sends the regenerated clock and received data to a voice compression expander (104) configured by the digital signal processor (DSP), and a coder-decoder (105) configured by the PCM codec.
The voice compression expander (104) carries out signal expansion processing, and the coder-decoder (105) decodes the expanded signal, converts it to an analog voice signal and sends it to a microphone-speaker audio component (106), where voice is generated.
Conversely, voice input from the microphone-speaker audio component (106) is changed into a signal, this signal is sent to the coder-decoder (105) for decoding, then sent to the voice compression expander (104), where it undergoes voice expansion processing and is sent to the signal processor (103).
The signal processor (103) modulates the signal for transmission, and sends it to the A/D, D/A converter (102).
The transmission voice signal converted to an analog signal by the A/D, D/A converter (102) is sent to the radio component, where it is up-converted and transmitted via the antenna.
The ASIC controller (107) controls each component in this portable radiotelephone. The ASIC controller and each of the other components operate by receiving power supplies from the power source (108).
The power source (108) is powered by a commercial power source (109) or a back-up battery (110), and this power source charges the back-up battery (110).
Program memory (111), in which programs are stored, SRAM (112), which is used as working memory, and an EEPROM (113) for storing abbreviated dialing data are connected to the ASIC controller (107), as are an LCD driver (115) for controlling the LCD (114), and a key input detection circuit (117) that detects key operations in the dial key-equipped key matrix (116), and sends to the ASIC controller (107) codes corresponding to the operated keys.
The ASIC controller (107) and the ASIC signal processor (103) comprise an integrated ASIC (118), and the LCD (114) and LCD driver (115) comprise a display component (119).
Mobile communication devices are generally equipped with AFC such as that depicted in FIG. 11. A received radio frequency signal (RF) is guided to a mixer (120), where it is down-converted to an intermediate frequency signal using output from a voltage controlled oscillator (VCO) comprising a local oscillator, then guided to a bandpass filter (BPF), which extracts the intermediate frequency signal (IF) to be sent to an orthogonal demodulator (123).
This IF signal is broken down into I-channel and Q-channel signals by the orthogonal demodulator (123), these signals are sent to respective low pass filters (124, 125), where unnecessary frequencies are removed, then to A/D converters (126, 127), where they are converted into digital data, then on to an orthogonal wave detector (128) in a modem (130).
In the orthogonal wave detector (128), I-channel data and Q-channel data are expressed as phase function data, and this phase function data is input to a frequency offset detector (129).
The frequency offset detector (129) detects frequency offset on the basis of the phase function data, that is, it performs phase offset detection, and detection results are sent to a D/A converter (131), where they are converted into a digital signal.
This digital signal is sent to a low pass filter (132), where it undergoes error integration, and the results are then input to the VCO (121).
The VCO (121) changes oscillation frequencies according to the voltage input, and sends the output to the mixer (120).
In this way, AFC is carried out on the frequencies of received signals, and requires feedback to reduce phase error.
Portable radiotelephones are also equipped with the above-described AFC, the AFC-related component of a conventional portable radiotelephone being configured specifically as shown in FIG. 12.
With this portable radiotelephone, the received signal (RSSI) level detected in advance by a diode (141) is digitized by an RSSI A/D converter (143) within an A/D-D/A block (142), the output from this A/D converter (143) is acquired by a diversity controller (144), which controls a PIN diode switch (SW) (145) on the basis of this value. The outcome of this determines the selection of one of the two antennas (147, 148) in the antenna component (146).
The transmitted signal is received by the antenna component (146), and the frequency of the received signal is down-converted by a first local oscillation synthesizer (151) and a second local oscillation synthesizer (152).
Bandpass filters (BPF) (153, 154) are provided to extract signals of the required frequency from the down-converted output of the respective synthesizers (151, 152) described above.
Output from this bandpass filter (154) is sent to an AFC circuit (155) indicated by a dotted line, and the orthogonal demodulator (156) in the AFC circuit (155) breaks this output down into I- and Q-channel analog signals (ARI, ARQ).
The analog signals (ARI, ARQ) are digitized by A/D converters (157, 158) in the A/D-D/A block (142), and sent to a delayed wave detector (159) in the signal processing block (160).
The delayed wave detector (159) expresses the I-channel data and Q-channel data as phase function data, and this phase function data is input to a frequency offset detector (161).
The frequency offset detector (161) performs frequency offset detection based on the phase function data, the results of this detection process are sent to a low pass filter (162) for error averaging, and then on to a D/A converter (163), where they are converted into an analog signal. This analog signal is then input to a VCTCXO (164), which is a voltage controlled oscillator.
The VCTCXO (164) oscillates by changing its oscillation frequency in accordance with the voltage input, and sends the output to a first local oscillation synthesizer (151), a second local oscillation synthesizer (152), and then, via a frequency divider and phase shifter, on to an orthogonal demodulator (156).
In this way, AFC is carried out on the frequencies of received signals, and requires feedback to reduce phase error.
However, because mobile communication devices such as the portable radiotelephone described above make use of techniques that gradually reduce frequency offset while providing feedback based on received signals, during checks to certify conformance to technical standards, for example, there are times when these mobile communication devices are unable to satisfy the specifications for technical standards conformance certification.
That is, during technical standards conformance certification testing, a frequency corresponding to a specific channel must be transmitted without a received signal, but since conventional mobile communication devices such as the one described above input the central value of the AFC signal into a VCTCXO (164), no consideration is given to the temperature characteristics, power fluctuations, load fluctuations, deformation over time or manufacturing irregularities of the VCTCXO, and no thought is given to condigit errors or convergence bias errors in the A/D converters, so that conventional mobile communication devices have not always been able to satisfy the specifications for technical standards conformance certification.